Fused salt electrolysis cell



Nov. 29, 1960 J. DQMUELLQER' EI'AL FUSED SALT'ELECTROLYSIS- CELL FiledDec. 23, 1958 Nov. 29, 1960 J. D. MUELLER ETAL 2,962,433

FUSED SALT ELECTROLYSIS CELL 2 Sheets-Sheet 2 Filed Dec. 23, 1958 FIG. 2

2,962,433 Patented Nov. 29, 1960 FUSED SALT ELECTROLYSIS CELL John D.Mueller and J. D. Russell, Baton Rouge, La.,

assignors to Ethyl Corporation, New York, N.Y., a corporation ofDelaware Filed Dec. 23, 1958, Ser. No. 782,540

2 Claims. (Cl. 204-247) This invention relates to an improved fused saltelectrolysis cell. More particularly, it relates to an improved fusedsalt electrolysis cell having an improved type of electrode constructionwhich provides increased current efliciency and other advantages.

Metallic sodium is generally obtained from the electrolysis of acomposition of chloride salts including sodium chloride. Theelectrolysis has been long since carried out in cells of the Downs type(US. Patent 1,501,756). This cell is characterized by a centrallypositioned bottom mounted vertically aligned graphite anode and asurrounding steel cathode of cylindrical shape having a slightly largerdiameter than the said graphite anode. These electrodes, thussubstantially concentrically mounted, define a narrow annular spacewithin which electrolysis occurs. A cylindrical foraminous diaphragm isalso usually concentrically positioned within the electrolysis zone,defined by said annular space, for the purpose of reducing the amount ofrecombination of the metallic sodium and chlorine after separation atthe anode and cathode, respectively.

During recent years 'a new type of cell, basically similar to the Downstype, has emerged. This new cell employs a plurality of bottom mountedvertically aligned graphite anodes which extend upwardly into a cathodeassembly having individual apertures or openings, the sides of whichsurround each of the said anodes in concentric fashion to formindividual annular electrolysis zones. As in the original Downs cell,foraminous metal diaphragms are generally placed within each of the saidannular electrolysis zones.

Both of these types of fused salt electrolysis cells have, in general,given good results. One disadvantage they possess, however, is thattheir current efficiency has been relatively low. Generally, the currentefiiciency of the average multiple electrode cell of the Downs typeranges between about 83 to 86 percent. In commercial establishmentsimprovement of current efiiciency is extremely important. Improvementson the order of only one percent can result in savings of many thousandsof dollars in a fair size commercial establishment. The problemsencountered in making any such improvements, however, are very numerous,difliicult and complex. Many approaches have been tried, most of themunsuccessful. But because of the importance of making thoseimprovements, a great expenditure of money and effort has been spent inorder to increase current efliciency. Various avenues have beeninvestigated to determine how this could be done. For example, certaincell bath compositions have been experimented with so that currentefiiciency may be increased in this manner. (See recently issued US.Patent 2,850,442.) One of the many factors which has been investigatedextensively because of the serious adverse effects on current efliciencyis that of calcium bridging. Precipitated calcium tends to form shortcircuits between the diaphragms and the cathodes, decreasing greatly thecell efliciency.

In view of this problem it is an object of this invention to provide animproved fused salt electrolysis cell for the production of metallicsodium, particularly an improved fused salt electrolysis cell whereinthe current efliciency is greatly improved over other cells of thistype. It is also an object of this invention to provide a cell whereinthe durability of the diaphragms are greatly improved. Yet anotherobject is to provide a cell wherein production of sodium and chlorine isincreased. Other objects will appear hereinafter.

The apparatus of the invention will be fully understood from thedescription hereinafter and from the figures illustrating the preferredembodiment, wherein: Figure 1 is a sectional elevation view of anembodiment of the invention which is a multiple electrode fused saltelectrolysis cell employing an embodiment of the invention, i.e. onehaving an eccentric anode-cathode type of construction. Figure 2 is across-sectional plan view taken along line 11 of Figure 1 showing theembodiment of Figure 1 in greater detail.

Broadly, the invention is a new and improved fused salt electrolysiscell of the multiple anode-cathode member type wherein the anodes, aswell as the cathode members, conform to a symmetrical plan usually atabout the center of the cell, but wherein the sum total effect is thatthe anodes and cathode members are offset from each other in eccentricfashion. Further, the eccentricity is such that between any given pairof anode-cathode members the distance between the centers of theopenings within the cathode members is less than the distance betweenthe corresponding anode centers. This will be more fully understood uponconsideration of the following statements. Thus, there is provided acell of the type wherein the cathode assembly has a plurality ofcylindrical openings and a plurality of vertically aligned bottommounted anodes having smaller cross-sectional diameters thanthe saidcathode cylindrical openings, said anodes extending upwardly into thesaid cathode cylindrical openings but leaving spaces which areelectrolysis zones having the cross-sectional configurations ofeccentric annuli. Providing further, that in all embodiments thenarrower sides of the said cross-sectional configurations are of greaterradial distance from the cell center than the wider portions of theannular electrolysis zones.

Several embodiments are possible but in all cases the narrower sideof'the eccentric annular shaped electrolysis zones will be generally orsubstantially away from the center of the cell. A preferred embodimentis one wherein the narrower sides of the eccentric annular shapedelectrolysis zones are approximately percent of the dimensions of thesides having the greatest dimensions. Ranges of from about 85 to aboutpercent are also generally satisfactory.

The principle of the invention and the embodiments thereof will be fullyunderstood from the following detailed description.

Figure l is asectional elevation view of the cell according to itspreferred embodiment. The plan disposition of the cell elements is morereadily seen in Figure 2 which shows a cross-sectional plan view, takenalong line 11 of Figure 1. Referring to Figure 1 and Figure 2 it is seenthat the wall of the cell includes an exterior cell shell of steel plate7, and a lining of refractory material 8. Centrally arranged, at thecorners of a square in the cell are four cylindrical graphite anodes 9 99 9 A cathode assembly 15 includes four generally cylindrical portions16 16 16 and 16 surrounding the individual anodes 9 and formingtherewith the eccentric annular electrolysis zones 17 17 17 17 intowhich the diaphragms (represented in Fig. 1 by broken lines) areextended. The cylindrical portions 16 16 16 16 of the cathode assembly15 are joined together by tangential connections and by webs. Electrodes26 26 extend from the cathode assembly 15 and project through theopenings 30 30 of the cell wall. The said openings are filled with acastable refractory material 31 31 The current is fed to the anodes 9 bythe anode bus bars 2 2 through electrical connections not shown. A domeand collector assembly is mounted centrally above the anode-cathodeelectrodes and includes a chlorine dome 3 in the form of an invertedgenerally conical member and a sodium collecting conduit 1?. Thechlorine dome terminates in a chlorine discharge line 5 the purpose ofwhich is to transfer the gaseous chlorine to subsequent operations. Thesodium collecting conduit 19 meets and is connected to a riser pipe 6.

The following working example is illustrative of a preferred mode ofoperating the invention.

In operation, the cell contains, up to a level approxi matelyintermediate the full vertical elevation of the chlorine dome 3, fusedelectrolyte chlorides which are referred to as a bath. This molten bathincludes not only sodium chloride but appreciable quantities of cal ciumchloride. The sodium and chlorine are released in the eccentric annularspaces between the anodes 9 and cathode members 16 and rise on oppositesides of the diaphragm. The sodium collects within the sodium collectingconduit 19 and the chlorine gas is evolved through the chlorine dome 3and discharge line 5.

Operation was continued in this manner for a period of 100 days. At thebeginning of this period the cell operated at a current efiiciency of 93percent and at the end of this time at a current efliciency of 87percent. The overall average current efficiency, or mean currentefficiency, was 90 percent. This compares with an average currentefliciency of generally about 86 percent for the ordinary cell havingconcentric anode-cathode members. Also an average greater overallproduction of metallic sodium, and chlorine, was produced. Productionwas greatly increased as contrasted with the production obtained inordinary cells having concentric anode-cathode members. It was alsofound that the operational life, or durability, of the diaphragms wasconsiderably increased. Thus, the new and improved cell according to thepresent invention provides definite advantages over fused saltelectrolysis cells built with concentric anode-cathode members.

Having thus described the invention and its best mode of operation, itwill be realized that some variation of the specific design of the cellis permissible, subject to the limitation that the electrolysis zonesformed between the anode-cathode members have the cross-sectionalconfigurations of eccentric annuli wherein the narrower sides of thesaid configurations are at substantially greater distances from thecenter of the cell than other portions of the said annuli. Of course itwill be realized that a cell can be constructed wherein the cathodecylindrical openings or apertures can be offset in preference to theanodes and the same result, as taught in the foregoing specification,obtained. Generally, the dimensions of the narrower side of theeccentric annuli should be approximately 90 percent of the widest sidesof the said electrol ysis zones or eccentric annuli.

Having fully described the apparatus what is claimed is:

1. An improved cell of the multiple electrode type for the electrolysisof fused salts, said cell comprising a unitary cathode structure havinga plurality of cylindrical apertures, said apertures having centerssubstantially equidistant from. the center of the cell and alsoconforming to a symmetrical plan about a line which is substantiallythrough the center of the cell and which bisects a line through thecenters of a pair of the cylindrical apertures, and a correspondingnumber of vertically aligned, bottom mounted anodes having smaller crosssectional diameters than the said cathode cylindrical apertures andprojecting upwardly into the said cathode cylindrical apertures andthereby forming annular electrolysis zones, the anode centers beingpositioned on a symmetrical plan which corresponds to and parallels butis larger than the cathode plan, said electrolysis zones definingeccentric annuli, the wider and narrower portions thereof being locatedsubstantially radially from the center of the cell, and the widerportions of the said eccentric annuli being located closer to the centerof the cathode structure plan than the narrower portions and thedimensions of the narrower sides of the electrolysis zones being fromabout to about 95 percent of the dimensions of the wider sides of thesaid electrolysis zones.

2. The apparatus of claim 1 wherein the dimensions of the narrowerportions of the electrolysis zones are about percent of the dimensionsof the wider portions of the electrolysis zones.

References Cited in the file of this patent UNITED STATES PATENTS2,648,631 Carlisle Aug. 11, 1953 2,887,448 Bergy et a1. May 19, 19592,893,940 Smith July 7, 1959

1. AN IMPROVED CELL OF THE MULTIPLE ELECTRODE TYPE FOR THE ELECTROLYSISOF FUSED SALTS, SAID CELL COMPRISING A UNITARY CATHODE STRUCTURE HAVINGA PLURALITY OF CYLINDRICAL APERTURES, SAID APERTURES HAVING CENTERSSUBSTANTIALLY EQUIDISTANT FROM THE CENTER OF THE CELL AND ALSOCONFORMING TO A SYMMETRICAL PLAN ABOUT A LINE WHICH IS SUBSTANTIALLYTHROUGH THE CENTER OF THE CELL AND WHICH BISECTS A LINE THROUGH THECENTERS OF A PAIR OF THE CYLINDRICAL APERTURES, AND A CORRESPONDINGNUMBER OF VERTICALLY ALIGNED, BOTTOM MOUNTED ANODES HAVING SMALLER CROSSSECTIONAL DIAMETERS THAN THE SAID CATHODE CYLINDRICAL APERTURES ANDPROJECTING UPWARDLY INTO THE SAID CATHODE CYLINDRICAL APERTURES ANDTHEREBY FORMING ANNULAR ELECTROLYSIS ZONES, THE ANODE CENTERS BEINGPOSITIONED ON A SYMMETRICAL PLAN WHICH CORRESPONDS TO AND PARALLELS BUTIS LARGER THAN THE CATHODE PLAN, SAID ELECTROLYSIS ZONES DEFININGECCENTRIC ANNULI, THE WIDER AND NARROWER PORTIONS THEREOF BEING LOCATEDSUBSTANTIALLY RADIALLY FROM THE CENTER OF THE CELL, AND THE WIDERPORTIONS OF THE SAID ACCENTRIC ANNULI BEING LOCATED CLOSER TO THE CENTEROF THE CATHODE STRUCTURE PLAN THAN THE NARROWER PORTIONS AND THEDIMENSIONS OF THE NARROWER SIDES OF THE ELECTROLYSIS ZONES BEING FROMABOUT 85 TO ABOUT 95 PERCENT OF THE DIMENSIONS OF THE WIDER SIDES OF THESAID ELECTROLYSIS ZONES.